Washington State University researchers have used a super-cold cloud of atoms that behaves like a single atom, opening a new experimental path to potentially powerful quantum computing.
Physicist Peter Engels and his colleagues cooled about one million atoms of rubidium to 100 billionths of a degree above absolute zero. There was no colder place in the universe, said Engels, unless someone was doing a similar experiment elsewhere on Earth or on another planet.
At that point, the cluster of atoms formed a Bose-Einstein condensate — a rare physical state predicted by Albert Einstein and Indian theorist Satyendra Nath Bose — after undergoing a phase change (similar to a gas becoming a liquid or a liquid becoming a solid).
Spin-orbit-coupled Bose–Einstein condensates (BECs) provide a powerful tool to investigate interesting gauge field-related phenomena. The research team studied the ground state properties of such a system and showed that it can be mapped to the well-known Dicke model in quantum optics, which describes the interactions between an ensemble of atoms and an optical field. A central prediction of the Dicke model is a quantum phase transition between a superradiant phase and a normal phase. They detected this transition in a spin-orbit-coupled BEC by measuring various physical quantities across the phase transition. These quantities include the spin polarization, the relative occupation of the nearly degenerate single-particle states, the quantity analogous to the photon field occupation and the period of a collective oscillation (quadrupole mode). The applicability of the Dicke model to spin-orbit-coupled BECs may lead to interesting applications in quantum optics and quantum information science.